1. Field of the Invention
The present invention relates to hydraulic lifts and to control systems for automatically correcting the level of a twin-post hydraulic cylinder lift platform, and more particularly, pertains to an electrohydraulic control system for detecting and correcting incremental changes in hydraulic lift platform level orientation without any potential damage to the platform or any object which may be located on the platform.
2. Discussion of the Prior Art
Hydraulic platforms are employed in a variety of applications requiring varying degrees of stability and lifting power. Thus, hydraulic lifting platforms are used in the most diverse applications which range from their use on loading docks to their employment on aircraft carriers. In all of these utilizations, it is necessary to maintain a level platform to prevent damage to any object being lifted or supported thereon, to prevent damage to the hydraulic lift structure itself, and to ensure the safety of the personnel operating and utilizing the lift.
There are numerous conditions under which a hydraulic platform may be caused to tilt in any particular direction. A clearly obvious reason for causing a platform to tilt is an unequal distribution or shifting of a load which is arranged on the platform, and this tilting situation may, at times, become unavoidable for certain lifting applications. Other conditions which may cause the platform to tilt are internally inherent to the system structure. Thus, the tilting can be a result of normal wear of parts at different wear rates over a lengthy period of time, hydraulic line breakage or leakage at one of the hydraulic cylinders, or a jammed or defective valve on one operating side of a hydraulic pump. Normal wear as defined herein includes wear of the moving parts of the pump, and wear of the internal parts of each hydraulic cylinder, such as the pistons, the cylinder walls and the seals. In addition, the normally encountered leakage rate of hydraulic fluid from each cylinder may be slightly different, and therefore, over a lengthy period of time, may result in a significant degree of tilt predicated on the cumulative effect of many cycles of operation.
Presently hydraulic lifts rely primarily on the physical construction of the lift itself in order to maintain the level condition of the platform. The stiffness and strength of the components constituting the hydraulic lift, as well as the pressure created by the hydraulic pump, impart the platform with a level lift. Moreover, most hydraulic lifts employ some type of mechanical safety stop or break to prevent extreme slippage of the platform. The mechanical safety stop or break may consist of a type of spring-loaded safety bar in the pistons or a separate support rack which is adapted to be positioned beneath the hydraulic lift. The safety stop or break which is used to prevent extreme slippage of the platform usually does not incorporate structure or function for preventing or correcting less severe degrees of tilting of the platform. Therefore, in the technology there is presently no structure available which will produce and maintain an exact degree of platform levelness required by certain lifting applications.